To use Goal Seek for a time series:
From any Strategic Finance view, select Analysis, then What if Analysis, then Goal Seek.
In To Values in Account, select a source account to contain the goal.
In By Changing Account, select the source account affecting the goal.
This account must be related to the goal account through a formula. To view account relationships to determine if there is such a formula, see Using Analyze.
In In Period and To, enter the years to change the source account.
Either use the returned adjustments in your mode or reject the results.